1. Field of the Invention
The present invention relates to a foot controller connecting to a sewing machine and more particularly to a foot controller connection error detection device to detect a contact failure between a plug provided on the foot controller and a jack provided on the sewing machine.
2. Description of the Related Art
Conventional types of embroidery machines or lock stitch sewing machines are provided with a needle bar drive mechanism provided in an arm of a sewing machine to vertically move the needle bar with a sewing needle attached and a loop taker and a speed adjustment dial to enable the setting of sewing speed. When the user operates a start/stop switch, the needle bar drive mechanism and the loop taker is driven via a sewing machine main shaft in a synchronized manner by a sewing machine motor. Therefore, utility patterns and embroidery patterns can be sewn on a fabric placed on a bed in a prescribed sewing speed.
The foot controller enables the user to give instructions to start a sewing process or adjust sewing speed even when the user's hands are occupied to hold the work fabric. A plug is provided on the end of a cord, extending from the body of the foot controller and the plug is connected to a jack provided in the body of the sewing machine. The user, by operating the foot controller with a depression of the foot can instruct the start of a sewing process and moreover change the sewing speed by the amount of depression.
For example, a safety device described in JP-A-1980-71186 is provided with a sewing machine motor, a speed controlling means to drive control the sewing machine motor and a speed instructing means etc. to provide speed instructing signals to the speed controlling means. When the user depresses the pedal provided on the speed instructing means, a resistance value of a variable resistor provided inside the speed instructing means is changed. When a speed instructing voltage corresponding to the resistance value is applied to the speed controlling means, the drive of the sewing machine motor is controlled in correspondence with the voltage (for example, refer to FIG. 1 and pages 6 to 7 of JP-A-1980-71186.).
That is, as shown in FIG. 8, a plug 111 is arranged on the end of a cord 120 connected to a foot controller 100 which serves as a speed controlling means. A first power line L1 and a first earth line L2 are arranged inside the cord 120, one end of which extends into the foot controller 100. Inside the foot controller 100, in between the first power line L1 and the first earth line L2, a resistance R3 (approximately 1 KΩ) and a variable resistor VR (maximum resistance value: approximately 10 KΩ) are connected in series. Also, the other end of the first power line L1 and the second earth line L2 are connected to the plug 111 respectively.
On the other hand, a second power line L3 and a second earth line L4 are arranged inside an electronic sewing machine M, both having one end connected to the jack 109 respectively. Also, the other end of the second power line L3 is connected to an analog signal input port AP of a microcomputer 16 mounted on a control base plate 115. On the second power line L3, a +5V of power voltage is applied via a pull-up resistance R1 (approximately 4.7 KΩ). The other end of the second earth line L4 is earthed.
The above described plug 111 is disconnect-ably connected to the jack 109, and on the microcomputer 116, the speed instructing voltage corresponding to the resistance value of the variable resistor VR is applied via the plug 111 and the jack 109.
In such configuration, since the foot controller 100 is not depressed at the point when the power is supplied into the electronic sewing machine M, the potential on a voltage dividing point P of the pull-up resistance R1, resistance R3 and variable resistor VR are small, hence a sewing machine motor 118 is not driven. However, when the user depresses the foot controller 100, the potential of the voltage dividing point P is changed corresponding to the amount of depression. The size of the drive voltage of the sewing machine motor 118 outputted from a drive circuit 117 also changes corresponding to the size of the potential. Therefore, the drive speed of the sewing machine motor 118 can be controlled in correspondence with the amount of depression of the foot controller 100. In this case, when a contact resistance Ra is generated between the first power line L1 and the second power line L3 and a contact resistance Rb is generated in between the first earth line L2 and the second earth line L4 due to time elapse, the contact state of a connector of the plug 111 and the jack 109 is impaired. Because the potential of the voltage dividing point P is increased by the sum of the two contact resistances Ra and Rb, a problem arises, in which the rotation speed of the sewing machine motor 118 exceeds the speed intended by the user.
Also, in case for example the plug 111 is not sufficiently inserted into the jack 109 and the contact of the plug 111 and the jack 109 is unstable, the total contact resistance value is rapidly increased or reduced. This leads to instability of the rotation speed of the sewing machine motor 118, thereby giving rise to the so called speed disparity problem.